(a) Field of the Invention
The present invention relates to a novel Pcr family gene which confers tolerance to heavy metal to organisms transformed with the Pcr family genes. More particularly, the present invention relates to a novel Pcr family gene which confers tolerance to heavy metal and transformed organisms using the gene thereby having improved resistance to and increased accumulation of toxic materials.
(b) Description of the Related Art
Heavy metals such as lead, cadmium, mercury and so on are major environmental toxicants, which cause reactive oxidation species generation, DNA damage, and enzyme inactivation by binding to active sites of enzymes in cells of living organisms.
Contamination of the environment with heavy metals has increased drastically due to industrialization and increase in population. Soils contaminated with heavy metals inhibit normal plant growth and cause contamination of foodstuffs. Many heavy metals are very toxic to human health and carcinogenic at low concentrations. Therefore removal of heavy metals from the environment is an urgent issue.
Studies for removing heavy metals from soil are actively progressing worldwide. Traditional methods of dealing with soil contaminants include physical and chemical approaches, such as the removal and burial of the contaminated soil, isolation of the contaminated area, fixation (chemical processing of the soil to immobilize the metals), and leaching using an acid or alkali solution. These methods, however, are costly and energy-intensive processes.
Living organisms have a mechanism for mitigating toxicity of materials using transporter proteins or biological materials having an affinity for noxious materials that invade the body. Use of genes contributing to living organism's resistance against noxious materials would provide an environmentally-friendly way to remediate environments polluted with noxious materials at a very low cost as compared with the physical and/or chemical remediation that is currently being employed (Mejare and Bulow, Trends in Biotechnology; 2001, Raskin I. and Ensley B. D. Phytoremediaton of Toxic Metals., John Wily & Sons, New York; 2000). In particular, as plants have many advantages such as their ability to express foreign genes readily and thus exhibit new phenotypes, they can be produced and maintained at a low cost, they are aesthetically pleasing, etc., research is being actively conducted on improvement of plants by inserting useful genes thereinto for use in environmental cleanup. This technique, the use of plants for cleaning up environment, is called “Phytoremediation.” Phytoremediation has recently been proposed as a low-cost, environment-friendly way to remove heavy metals from contaminated soils. It is a relatively new technology for cleanup of contaminated soil that uses general plants, specially bred plants, or transgenic plants to accumulate, remove, or detoxify environmental contaminants. The phytoremediaton technology is divided into phytoextraction, rhizofiltration, and phytostabilization. Phytoextraction is a method using metal-accumulating plants to extract metals from soil into the harvestable parts of the plants; rhizofiltration is a method using plant roots to remove contaminants from polluted aqueous streams; and phytostabilization is the stabilization of contaminants such as heavy metals in soils to prevent their entry into ground water using plants.
Experiments were conducted to produce transgenic plants with improved capacity for phytoremediation. They used genes that confer resistance to heavy metals. Examples of heavy metal resistant genes are ABC (ATP Binding Protein) transporters such as YCF1, CAX2 (Calcium exchanger2), Cytochrome P450, NtCBP4 (Nicotiana tabacum calmodulin-binding protein), phytochelatin, glutathione synthetase, MerB (Organomercurial lyase) and so on. Since there are many different locations in the world that need phytoremediation, and since they are different in physical and biological conditions, there is a need to produce many different kinds of plants that can remediate the environment under different local conditions. Therefore, it is necessary to develop many transgenic plants transformed with diverse genes that work by different mechanisms that result in improved resistance to heavy metals and toxic compounds.